Video-calls are calls comprising both video data and audio data. Typically the video data is the data of a transmitting user and the audio data is the voice data of the transmitting user. However, video-calls can comprise video of subjects other than the transmitting user, may comprise video of office documents during a video-conference, or may comprise a composite of inputs from multiple video cameras. Similarly, the audio data may comprise audio data other than the voice data of the transmitting user, including music, and supplemental audio effects.
Presently, mobile client devices have come to be increasingly sophisticated. Many smart-phones have multiple video cameras, microphones and relatively large video screens. Mobile tablet computers have similar capabilities with larger video screens. Accordingly, users have come to expect video-call capability.
However, evolving mobile wireless networks were originally designed to carry voice data. In contrast, a video call, in particular the video data portions comprise an amount of data large compared to the capacity of voice networks. Accordingly, the audio data and the video data may be sent over different communications transports.
Correspondingly, the receiving client device will have to combine the video data and the voice data arriving over different communications transports and to synchronize the two. However, since different communications transports have different characteristics and different synchronization techniques. Present synchronization techniques do not provide sufficient quality of experience for users for video-calls over heterogeneous transports.